Coldcard Firmware Flaw Enabled $70M Bitcoin Heist in 41 Minutes
CriticalWhat happened
An attacker drained 1,196 Bitcoin addresses in 41 minutes on July 30, stealing 1,082.65 BTC worth about $70.2 million. Galaxy Research mapped the sweep and linked it to a firmware flaw in Coinkite's Coldcard Bitcoin hardware wallet.
A March 2021 integration error routed seed generation to a deterministic software PRNG (MicroPython's Yasmarang fallback) instead of the STM32 hardware RNG. The fallback was seeded only from the chip UID and timer registers with no fresh entropy afterward, yielding roughly 40 bits of effective entropy on Mk3 and about 72 bits on later models—far below a proper BIP-39 seed. An attacker who can constrain the UID, timer state, and prior RNG history can offline-generate candidate seeds, derive addresses, and match them against the public blockchain.
Who is affected
Owners of Coldcard hardware wallets (Bitcoin-only devices from Coinkite) whose seeds were generated on vulnerable firmware. Affected versions include Mk2/Mk3 4.0.0–4.1.9 (fixed in 4.2.0), Mk4/Mk5 before 5.6.0, Q before 1.5.0Q, and corresponding edge builds.
Exposure is determined by the firmware present at seed creation time, not the currently installed version. Coinkite estimates thousands of devices could be in scope depending on production and usage patterns; TAPSIGNER, OPENDIME, and SATSCARD use different codebases and are unaffected.
Why it matters
Hardware wallets are marketed as the gold standard for cold storage of high-value crypto. A deterministic, low-entropy seed generation path turns that assumption into a catastrophic failure mode: funds can be swept en masse without physical access once seeds are reconstructed offline.
The speed and scale of the theft (over $70M in under an hour) demonstrate how blockchain transparency plus weak entropy enables fully automated, high-confidence attacks. Restoring an old seed to patched firmware or another wallet simply carries the weakness forward.
How it could have been prevented
Install Coinkite’s emergency firmware released July 31 for every affected model and track. Generating a new seed on the patched firmware and transferring coins is required; updating alone does not fix an existing weak seed.
Prefer seeds created with at least 50 fair, independent, private dice rolls. A strong unique BIP-39 passphrase adds a layer but Coinkite still recommends full seed replacement. Multisig only helps if the quorum is not composed entirely of affected Coldcards. Treat any seed created on the vulnerable path as compromised and migrate immediately.
Relevant professional terms
- Hardware wallet
- A physical device that stores cryptocurrency private keys offline, signing transactions without exposing the keys to an internet-connected computer.
- Pseudorandom number generator (PRNG)
- An algorithm that produces a deterministic sequence of numbers that appear random; if seeded with insufficient entropy it becomes predictable and undermines cryptographic security.
